Field of the Invention
The present invention relates to a thermal type flow sensor having a temperature sensor, which is arranged on an upstream side of a flow path through which a fluid flows, and a heating element disposed on a downstream side of the flow path.
Description of the Related Art
With a thermal type of flow sensor, a temperature sensor is disposed on an upstream side of a flow path through which a fluid flows, and a heater (heating element) is disposed on a downstream side of the flow path. In addition, the fluid is heated by the heater, whereas based on the temperature of the fluid as measured by the temperature sensor, a flow velocity or a flow rate of the fluid is detected.
This type of thermal sensor is used in a condition of being attached to a body or the like so that the flow path extends along a horizontal direction. Therefore, the fluid flows in a horizontal direction.
When the installation space is too narrow to orient the flow path in a horizontal direction, depending on the circumstances, it is inevitable that the thermal type flow sensor will have to be used in a posture such that the flow path extends along a vertical direction. However, when the temperature sensor is positioned at an upward location and the heater is positioned at a downward location, in the fluid, which is heated at the downward location and undergoes a rise in temperature, convection is generated accompanying rising of the fluid inside the flow path. At this time, if the fluid, which has risen in temperature, comes into contact with the temperature sensor, the temperature sensor also detects the temperature of the fluid rising upward. As a result, a defect is brought about in that the accuracy in detecting the flow velocity or the flow rate of the fluid is lowered.
Thus, in Japanese Laid-Open Utility Model Application Publication No. 06-080130, there has been proposed a mass flow meter in which a pair of temperature sensors are arranged horizontally when the body extends along a vertical direction.